EKG machines produce electrocardiograms representing the functioning of a patient's heart from electrical signals supplied by as many as twelve electrodes conductively attached to selected points on the patient's body. If the patient should require resuscitation with a defibrillator while the EKG machine is in operation, some means must be provided for protecting the EKG machine from the high energy electrical pulses that are applied to the patient by the defibrillator. Need for such protection would be unnecessary if the EKG electrodes were removed prior to the application of the defibrillator pulses, but that is not practical because there is often insufficient time. Most EKG machines are equipped with internal circuits that bypass the front end amplifiers in the presence of a defibrillation pulse, but full protection of the machine requires that voltage limiting means be included in each of the leads from the machine to the electrodes attached to the patient's body. Heretofore, this has been accomplished by inserting 6800-ohm, 2-watt carbon composition resistors in series with each lead. The resistors are generally mounted in the yoke at the end of the trunk cable from the machine. In a twelve-lead system, the yoke is heavy and awkward, especially in stress testing where the patient is moving and the yoke must be attached to his body. Furthermore, cables with yokes for this purpose are costly to build.